1. Field of the Invention
The present invention relates to a flowmeter element, a mass flowmeter and a mass flow measurement system, which are used for measuring a mass flow rate of fluid.
2. Description of Related Art
JP-A-2004-125804 discloses an ultrasonic flowmeter for measuring an amount of fluid flowing in a pipe by using ultrasonic wave. The ultrasonic flowmeter includes a first ultrasonic unit and a second ultrasonic unit. The first ultrasonic unit is disposed at an upstream side of a flow measurement part of the pipe, and the second ultrasonic unit is disposed at a downstream side of the flow measurement part of the pipe. The first and second ultrasonic units obliquely oppose to each other across the pipe. The amount of fluid flowing in the pipe is calculated based on a difference in transmission times needed for transmitting ultrasonic wave between the first and second ultrasonic units. That is, ultrasonic wave sent from the first ultrasonic unit takes a first transmission time to be received by the second ultrasonic unit, and ultrasonic wave sent from the second ultrasonic unit takes a second transmission time to be received by the first ultrasonic unit. A velocity of fluid is calculated based on the difference between the first and second transmission times. A volume flow rate of fluid is calculated by multiplying the velocity of fluid by a cross-sectional area of the flow measurement part of the pipe.
However, a mass flow rate of fluid cannot be calculated in the above ultrasonic flowmeter, although the above ultrasonic flowmeter can measure the volume flow rate of fluid. In order to calculate the mass flow rate of fluid, a pressure of fluid has to be measured. If a pressure detecting unit for measuring the pressure of fluid is arranged in the flow measurement part of the pipe, a space for locating the pressure detecting unit is needed in the flow measurement part of the pipe.